A number of applications exist for blending and mixing two or more fluids in controlled proportions for supply to a common output. Such applications include the blending and mixing of fire-retardant chemicals with water for extinguishing various types of fires and the blending and mixing of different components of fertilizers and insecticides with one another and with a carrier for application simultaneously as a composite mixture having fixed proportions of each of the different components. Such systems generally use a pump on the outlet conduit downstream from the blender for controlling the flow rate at which the blended mixture is applied.
Various types of mixing valves and blender devices have been devised in the past for use in such applications. A serious disadvantage of known systems, however, is that the accuracy of the ratio of fluids supplied through the output conduit for application is not constant but, instead, varies as the flow rate through the pump varies. In addition, the ratio of the amount of the different fluids in the blended output also varies as a function of the changes in head pressure of the fluids supplied to such prior-art blenders.
The inability of prior-art blenders to maintain the same ratio of fluids blended in spite of variations in the different head pressures of the fluids supplied to the blenders and in spite of variations in the flow rate or demand out of the blender through the pump controlling the flow is unacceptable for many applications. As a compromise, to overcome such shortcomings, stringent requirements often must be placed on the pressures of the fluid supplies; and the range of flow rate through the output pump must be limited. Placing these limitations on a blender system substantially reduces its versatility; and often it still is impossible to attain the desired uniformity in the blended output mixture, even if such limitations are placed on the system operation. Obviously, variations in the ratio of the blended mixtures can have substantial adverse effects, in terms of controlling the costs of the product used and in controlling the effectiveness of the resultant mixture for the purpose intended. As a consequence, it is desirable to be able to blend or proportion two or more fluids in an accurate ratio irrespective of variations in the pressures of the fluids supplied to the blender and over a wide range of flow rates from the blender in a simple and efficient manner.